Listen closely. When Max returns with the diesel, it's very clear the rig uses an air starter. It sounds like an air wrench, even on screen. The batteries are only used for the signals and lights. An old style diesel like this had no electronics. The only way to stop the engine is to shut off the fuel. I have a truck like this and a dozer. Both shut off the same way. Even modern diesel have fuel shut off switches , but they are operated electronically.

The air started would be the way to go in a post apocalyptic world. It's possible to re-pressurize the holdover tank with a bicycle air pump. It would take a while and a lot of work, though. Older diesels like this would also be very tolerant of sub-standard fuel. The filters would need to be drained regularly and re-installed. I'd dust out the air filter at every stop. Dirt coming through the intake will kill a diesel engine.